daniel_gudman said:
Photons (and other bosons)
Phonons (and other quasiparticles)
Compared to the "things" made of fermions...
Son, I am disappoint.
1)
You seem to think that bosons are not things.
Obvious counter-example: helium atoms in ground state. That's why they can form Bose-Einstein condensates. Many other things as well, as would be completely obvious from undergraduate QM.
2)
You seem to think that photons are energy.
Photons are quanta of the electromagnetic field. That's exactly what they are. They have three quantum numbers from the PoincarÚ group dictated by special relativity: mass, spin, parity.
Get it straight: photons are not energy. They
have energy. Energy is a
property that these things happen to have. This is not a conceptually complicated distinction. They have
other properties as well, e.g., momentum and spin. So why isn't anyone saying that photons "are" momentum instead? Why not photons "are" spin? Not that it'd be right, but at least the latter would be an intrinsic, frame-independent property that characterizes photons--a slight step up on objectivity. Oh wait, that's right: that would go against the retarded energy fetishism thing people have going.
3)
You seem to believe that quasiparticles are always bosons.
Go study, for example, semiconductors. (Well, maybe you don't, but it's not clear to me why this is even here.)
daniel_gudman said:
I've been keeping mostly quiet, but it's getting increasingly clear to me, that there are two groups of people here: The blind, and those with half an eye.
Sad.
daniel_gudman said:
I mean, if you're going to go with the classical mechanics definition of "energy is the capacity of a system to perform work"...
Don't forget that the classical mechanic interpretation was decisively proven incomplete over a century ago. That's the quantum revolution.
Stop talking like the convenient approximation is the actual truth.
Nothing in my previous post necessitated classical mechanics: my statements were applicable to physics in general, classical or quantum. The fact that you even bring it up is yet more evidence of just how poor your understanding of quantum mechanics is.
daniel_gudman said:
Also, speaking of classical mechanics, ...
Ok, fine: since you insist, let's talk about classical mechanics, in the simpler semi-general case. You have physical system, whose possible states are points in the
phase space comprised of generalized positions and momenta (q^k;p_k), so that the time evolution of the system traces out some curve determined by the initial state and the Hamiltonian flow.
What's energy? Some particular observable, depending on the kind of energy we're talking about. What's an observable?
A function over the phase space. For example, for the simplest case of a particle in one dimension, the kinetic energy is T(q;p) = p?/2m. If it's in a scalar potential, it's simple to add to this to get mechanical energy, etc. As for QM? Well, the observables form a commutative C*-algebra (cf. Poisson bracket), and quantumness happens whenever this algebra is non-commutative instead. It's possible to deform it: imposing [q,p] = i? gives us a non-commutative C*-algebra of formal observables, which by Gel'fand-Na?mark theorem is realizable as an algebra of operators on some Hilbert space.
So we come to the
very first thing anyone who studies QM proper learns: observables are operators on a Hilbert space that is the quantum-mechanical phase space. Hell, this is taken as an axiom in general quantum theory: it is literally part of what it means for physics to be "quantum". And even if one doesn't know any algebraic motivations (which never appear in introductory texts), that fact alone should make it
really obvious that energy is a
property of physical systems: more formally, an observable.
daniel_gudman said:
"Electricity" being "Energy" is built into the definition derived from the units.
Sheesh.
I can't even begin to apprehend the total confusion of ideas that could produce such a statement, but hopefully the following illustration will correct them:
Code:
á á á á á á á á á á á+-----------------------------+
á á á á á á á á á á á| Properties stuff can have á |
+--------------+ á á | á á á á á á á á á á á á á á |
| Stuff/Things | <-- | (Current, voltage, energy, á|
+--------------+ á á | áMomentum, Spin, Charge...) |
á á á á á á á á á á á+-----------------------------+
á Not a fucking complicated distinction.
Statement: "The pen is blue."
(Thing: Pen) <-- (Property: Blueness)
Herp.
Statement: "A 1.4 GeV proton hits your forehead."
(Thing: Proton) <-- (Property: Energy)
Derp.